A pet door allows convenient access of a pet to a home, however unrestricted access can lead to problems. For example, pets from neighbouring homes or other animals may also access the house, eating food or leaving mess. Furthermore, if the pet door is large enough, for example for a large dog, then this can be a security hazard, allowing access to people as well as animals. It is therefore desirable to limit access to the owner's pets only.
Controlled access pet doors are well known, including doors that open in response to a tag worn by the animal, for example on a collar. Examples of tags include a magnet, an infra-red transmitter, a radio transmitter, and a passive radio transponder worn by the pet. Examples of such systems may be found in the following references: US2002011217, GB2393245, JP4031580, and U.S. Pat. No. 4,497,133.
Another option for the animal tag is radio frequency identification (RFID). This may take the form of a collar-mounted tag or a transponder that is implanted under the skin of the animal. This latter case has the advantage of achieving controlled access without the animal having to wear a collar and external tag; these can become lost or snagged on branches, etc. Pet doors operating on RFID tags or sub-dermal transponders are well known, for example DE4124143, U.S. Pat. No. 5,992,096, U.S. Pat. No. 6,297,739, GB2376977, GB2381180, U.S. Pat. No. 6,944,990, US2004/0100386, GB2431431, GB2430331, PCT/GB2007/050540.
Pet doors that provide controlled access are preferably powered by batteries with a long lifetime. It is therefore important to minimise power to extend lifetime. When an ID tag is supplied with the pet door then the system can be optimised for that tag, only using sufficient power for reliable operation. However, operation with sub-dermal transponders that may already be in the animal for ID purposes presents additional challenges that reduce battery life.
An international standard for pet microchipping (ISO11785) has been adopted in many countries around the world. This standard recommends a full-duplex (FDX) transponder operating at a frequency of 134 kHz, and with a defined modulation scheme. However, many transponders that are present or still being implanted in animals do not adhere to this standard. The most notable example of this is the USA where the ISO standard is not well established at the time of this application. In the USA there are a range of different transponders in operation that encode the ID number in different ways and may operate at different frequencies; examples of common frequencies are 125 kHz, 128 kHz, and 134 kHz. In addition to full duplex transponders there are also half duplex transponders. Even in countries that have adopted the ISO standard there are still legacy chips in place that present the same problem of transponders that operate at different frequencies and have different coding schemes.
In order to determine the ID code of an arbitrary transponder a single read at one frequency may be carried out. However this can only match one transponder frequency and transponders designed to operate at other frequencies will be limited in range. In order to achieve adequate read range for all transponders the reader field would have to be raised to high levels, drawing high levels of power.
An alternative that allows the reader to work with a wide population of transponders in various countries is to operate with multiple frequencies and multiple modulation schemes. Testing for all transponders would therefore require repeated measurements, again drawing high levels of power.
Another feature of the set of transponders implanted into pets is that their ranges are not identical. For example, the technology has become better optimised over time, meaning that older transponders tend to have reduced range. In order to work with as wide a population as possible there is a requirement for high reading fields. The amplitude of the reader field may be set high, so that there is adequate range for the worst case transponders. However, this has the drawback that high levels of power would be required.
In summary, an RFID pet door that works with a wide range of different transponders that are present in animals can require high levels of power, and a correspondingly short battery life. There is therefore the need for such an RFID pet door with improved efficiency for a given range, or equivalently improved range for a given efficiency.